As four AA batteries commercially available are used today as a power source for most of on-camera flashes, the cavity to accommodate the batters typically consists of four small independent AA battery-containing cavities. Although such an arrangement is able to prevent physical contacts therebetween which would otherwise disrupt normal use (the worn surfaces of batteries are liable to trigger short circuit when they contact each other), its problem lies in long recycle time and less number of flashes.
The Chinese utility model patent with the No. 201320787015.8 discloses on-camera flash with a double-battery structure including a holder and a head which is hinged to the holder and can rotate relative to the holder; a battery-containing cavity is formed in the holder, a cover is provided at the inlet of the battery-containing cavity; a first battery cartridge accommodating some AA batteries is also included, at least first input electrical plug is contained in the battery-containing cavity; when the first battery cartridge is installed in the battery-containing cavity, a first output electric plug of the first battery cartridge and the first input electrical plug form an electrical connection which is characterized by including a second battery cartridge, and the second battery cartridge includes a lithium battery and can replace the first battery cartridge to plug in the battery-containing cavity; a second output electrical plug is installed on a housing of the second battery cartridge which is electrically connected with the control circuit installed in the holder via the second output electrical plug, thus solving the problems of long recycle time and less number of flashes. Such a structure, however, is complex and inconvenient because it requires the first battery cartridge for placing the AA batteries when using AA batteries, and also it involves two steps to install batteries during the use thereof.